MPLS is an abbreviation of Multi-Protocol Label Switching. MPLS makes use of short labels with fixed length to encapsulate packets, and achieves quick forwarding at a data plane. At a control plane, MPLS possesses strong and flexible routing functionality of IP network, and can satisfy requirements of various new applications on the network.
Such technique was initially proposed in order to enhance the forwarding speed of the router. In comparison with a traditional IP routing mode, in the technique, during forwarding data, only at the network edge is an IP message header analyzed, while the IP message header does not need to be analyzed at each hop, thus reducing the processing time.
With the development of the ASIC technology, the routing searching speed is no longer a bottleneck blocking development of the network. This makes unobvious the advantage of MPLS in terms of enhancing the forwarding speed. However, the characteristics of MPLS in supporting multilayer labels and connection oriented forwarding plane enable MPLS to be widely applied in such aspects as virtual private network (VPN), traffic engineering and quality of service (QoS), etc.
MPLS performs forwarding on the basis of labels, and assignment as well as distribution of MPLS labels can be statically configured or achieved via such protocols as LDP, RSVP-TE and BGP, etc. RSVP-TE is mainly used to achieve the establishment of TE LSP, LDP can be applied in the establishment of LSP with topologically driven route or serve as a signaling protocol of the pseudo-wire (PW) label in L2VPN, and the border gateway protocol (BGP) mainly extends the signaling protocol serving as the private network routing label under VPN and establishes LSP of the label routing under a cross-domain VPN.
Currently, the BGP protocol running on a certain device distributes, only according to a specific service element, such as VPN routing, a VPN instance, a VPLS instance, etc., the same one MPLS label or the same one group of MPLS labels corresponding to the service element to all other devices having established BGP protocol neighborhood with the current device.